Honeycomb structure

ABSTRACT

Provided is a honeycomb structure including a honeycomb substrate having partition walls defining cells extending from an inflow end face to an outflow end face, and plugging portions. The cells include at least one cell group consisting of a both-end plugged cell, an inlet cell adjacent to the both-end plugged cell, and an outlet cell adjacent to the both-end plugged cell. The partition walls defining the both-end plugged cell have a first common partition wall defining both of the inlet cell and the both-end plugged cell, and a second common partition wall defining both of the outlet cell and the both-end plugged cell. A first flow-through hole is formed in an end portion of the first common partition wall on the outflow end face side, and a second flow-through hole is formed in an end portion of the second common partition wall on the inflow end face side.

The present application is an application based on JP-2014-033448 filedon Feb. 24, 2014 with the Japanese Patent Office, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a honeycomb structure, and moreparticularly, relates to a honeycomb structure which is excellent intrapping efficiency and inhibits an increase of pressure loss when ashis accumulated.

2. Background Art

Heretofore, for the purpose of removing particulates (hereinafter alsoreferred to as PM (Particulate Matter)) included in exhaust gasdischarged from various engines and the like, exhaust gas purifyingdevices including honeycomb structure filter (honeycomb structure) havebeen used. There is known a honeycomb structure including a honeycombstructured honeycomb substrate and plugging portions disposed at openends of inlet cells which are predetermined cells of this honeycombsubstrate on the outflow end face side thereof and at open ends ofoutlet cells which are the residual cells on the inflow end face side(e.g., see Patent Documents 1 and 2). Specifically, the honeycombsubstrate has porous partition walls defining a plurality of cells whichform through channels for the exhaust gas.

When the exhaust gas including particulates flows into the honeycombstructure from the inflow end portion side which is one end portion, theexhaust gas is filtered by the partition walls to remove theparticulates and purified gas is discharged from the outflow end portionside which is the other end portion. In such a manner, exhaust gas ispurified by the honeycomb structure.

When the exhaust gas flows into the inlet cells of the honeycombstructure, the exhaust gas passes through the partition walls definingthe inlet cells to flow into the outlet cells, since the open ends ofthe inlet cells on the outflow end face side are plugged. Furthermore,the open ends of the outlet cells on the inflow end face side areplugged, and hence the purified gas is discharged from the open ends onthe outflow end face side. The PM accumulated in the honeycomb structureis burnt by raising the temperature of the exhaust gas every appropriateinterval or by heating with an electric heater or the like. As describedabove, the PM is prevented from being excessively accumulated in thehoneycomb structure.

Furthermore, some other honeycomb structures having plugging portionsdisposed only at one end portion or at the other end portion in order toprevent increase of pressure loss (e.g., see Patent Documents 3 and 4).

[Patent Document 1] JP-A-S49-038266

[Patent Document 2] JP-A-S56-148607

[Patent Document 3] JP-A-2003-035126

[Patent Document 4] JP-A-2004-108203

SUMMARY OF THE INVENTION

However, in honeycomb structures described in Patent Documents 1 and 2,one open end or the other open end of each cell is plugged, and hencepressure loss noticeably increases. Furthermore, when ash which is anoncombustible substance included in PM is accumulated, such accumulatedash is hard to be discharged from the honeycomb structure. Therefore,the pressure loss when ash is accumulated also noticeably increases. Ina honeycomb structure described in Patent Document 3, there are cells inwhich no plugging portion is disposed, and hence as compared with thehoneycomb structures described in Patent Documents 1 and 2, less ash isaccumulated, and the pressure loss increase is low. However trappingefficiency of PM is deteriorated. In a honeycomb structure described inPatent Document 4, similarly to Patent Document 3, there are cells inwhich no plugging portion is disposed, and hence the pressure lossincrease is low, however as compared with the honeycomb structuresdescribed in Patent Documents 1 and 2, the trapping efficiency of PM isdeteriorated. Further, in the honeycomb structure described in PatentDocument 4, the plugging portions are disposed in the cells on theoutflow end portion side, and hence ash is easily deposited in theoutflow end portion of the honeycomb structure. Ash deposited in thisportion is hard to be discharged. In consequence, when the deposited ashis not discharged, the pressure loss disadvantageously increases. On theother hand, a great deal of labor is required to discharge ash.

In consequence, there has earnestly been desired development of ahoneycomb structure which has a favorable trapping efficiency andinhibits increase of pressure loss when ash is accumulated.

The present invention has been developed in view of such problems ofconventional technologies, and an object thereof is to provide ahoneycomb structure which has a favorable trapping efficiency andinhibits increase of pressure loss when ash is accumulated.

According to the present invention, a honeycomb structure described inthe following is provided.

[1] A honeycomb structure including a honeycomb substrate havingpartition walls defining a plurality of cells which form throughchannels for a fluid and extend from an inflow end face as one end facewhere the fluid flows in to an outflow end face as the other end facewhere the fluid flows out, and plugging portions disposed at open endsof the cells of the honeycomb substrate, wherein the plurality of cellsinclude at least one cell group consisting of three cells which are aboth-end plugged cell in which the plugging portions are disposed atboth open ends on the inflow end face side and the outflow end faceside, an inlet cell which is adjacent to the both-end plugged cell andin which the plugging portion is only disposed at the open end on theoutflow end face side, and an outlet cell which is adjacent to theboth-end plugged cell and in which the plugging portion is only disposedat the open end on the inflow end face side, the partition wallsdefining the both-end plugged cell constituting the cell group have afirst common partition wall which is a common partition wall definingboth of the inlet cell and the both-end plugged cell, and a secondcommon partition wall which is a common partition wall defining both ofthe outlet cell and the both-end plugged cell, a first flow-through holeis formed in an end portion of the first common partition wall on theoutflow end face side, and a second flow-through hole is formed in anend portion of the second common partition wall on the inflow end faceside.

[2] The honeycomb structure according to the above [1], wherein in across section of the honeycomb substrate which is perpendicular to anextending direction of the cells, the inlet cell, the both-end pluggedcell and the outlet cell constituting each of the at least one cellgroup are arranged so that a first center which is the center of theinlet cell, a second center which is the center of the both-end pluggedcell and a third center which is the center of the outlet cell arepositioned on a same straight line.

[3] The honeycomb structure according to the above [1], wherein in thecross section of the honeycomb substrate which is perpendicular to theextending direction of the cells, the inlet cell, the both-end pluggedcell and the outlet cell constituting each of the at least one cellgroup are arranged to form an L-shape.

[4] The honeycomb structure according to any one of the above [1] to[3], wherein an open area of the first flow-through hole is from 0.3 to3.5 times as large as an average value of sectional areas in thedirection perpendicular to the cell extending direction of the inletcell, the both-end plugged cell and the outlet cell constituting thecell group.

[5] The honeycomb structure according to any one of the above [1] to[4], wherein an open area of the second flow-through hole is from 0.3 to3.5 times as large as the average value of the sectional areas in thedirection perpendicular to the cell extending direction of the inletcell, the both-end plugged cell and the outlet cell constituting thecell group.

[6] The honeycomb structure according to any one of the above [1] to[5], which is made of a porous ceramic material.

[7] The honeycomb structure according to any one of the above [1] to[6], wherein the honeycomb substrate is integrally formed.

[8] The honeycomb structure according to any one of the above [1] to[6], wherein the honeycomb substrate has a segment structure constitutedof a plurality of honeycomb segments.

A honeycomb structure of the present invention has a trapping efficiencyof the same degree as a trapping efficiency of a conventional honeycombstructure. That is, the honeycomb structure of the present invention isexcellent in trapping efficiency. Furthermore, the honeycomb structureof the present invention has cell groups including three specific cells,and first flow-through holes and second flow-through holes are formed inpredetermined partition walls, respectively. That is, in the honeycombstructure of the present invention, spaces where ash is deposited arepresent at two positions; at an end portion on the outflow end face sideand at an end portion on the inflow end face side (see symbols X and Yof FIG. 2). Furthermore, in the honeycomb structure of the presentinvention, the ash which is accumulated in the honeycomb structuresuitably joins a flow of an exhaust gas to be discharged outside along aroute of an inlet cell, a both-end plugged cell and an outlet cell.Therefore, the honeycomb structure of the present invention inhibits anincrease of a pressure loss when the ash is accumulated. As a result,maintenance operations when the ash is accumulated are performed lesstimes, i.e., the maintenance operation may scarcely be needed to beperformed. That is, the honeycomb structure is so-called free ofmaintenance in regard to deposition of ash.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing one embodiment of ahoneycomb structure of the present invention;

FIG. 2 is a sectional view schematically showing a cross sectionparallel to an extending direction of cells in the one embodiment of thehoneycomb structure of the present invention;

FIG. 3 is an enlarged view schematically showing an enlarged part of across section perpendicular to the cross section shown in FIG. 2;

FIG. 4A is a plan view schematically showing an example of arrangementpatterns of cell group in the honeycomb structure of the presentinvention;

FIG. 4B is a plan view schematically showing another example of thearrangement patterns of a cell group in the honeycomb structure of thepresent invention;

FIG. 4C is a plan view schematically showing still another example ofthe arrangement patterns of a cell group in the honeycomb structure ofthe present invention;

FIG. 4D is a plan view schematically showing a further example of thearrangement patterns of a cell group in the honeycomb structure of thepresent invention;

FIG. 4E is a plan view schematically showing a further example of thearrangement patterns of a cell group in the honeycomb structure of thepresent invention;

FIG. 4F is a plan view schematically showing a further example of thearrangement patterns of a cell group in the honeycomb structure of thepresent invention;

FIG. 4G is a plan view schematically showing a further example of thearrangement patterns of a cell group in the honeycomb structure of thepresent invention;

FIG. 4H is a plan view schematically showing a still further example ofthe arrangement patterns of a cell group in the honeycomb structure ofthe present invention;

FIG. 5A is a plan view schematically showing an example of arrangementpatterns of cell groups in the honeycomb structure of the presentinvention;

FIG. 5B is a plan view schematically showing another example of thearrangement patterns of cell groups in the honeycomb structure of thepresent invention;

FIG. 6A is a plan view schematically showing an example of arrangementpatterns of cell groups in the honeycomb structure of the presentinvention;

FIG. 6B is a plan view schematically showing another example of thearrangement patterns of cell groups in the honeycomb structure of thepresent invention;

FIG. 7A is a plan view schematically showing an example of arrangementpatterns of cell groups in the honeycomb structure of the presentinvention;

FIG. 7B is a plan view schematically showing another example of thearrangement patterns of cell groups in the honeycomb structure of thepresent invention;

FIG. 8 is a plan view schematically showing an example of arrangementpatterns of cell groups in the honeycomb structure of the presentinvention;

FIG. 9 is a plan view schematically showing an example of arrangementpatterns of cell groups in the honeycomb structure of the presentinvention;

FIG. 10 is a plan view schematically showing an example of arrangementpatterns of cell groups in the honeycomb structure of the presentinvention;

FIG. 11A is a plan view schematically showing an example of arrangementpatterns of cell groups in the honeycomb structure of the presentinvention;

FIG. 11B is a plan view schematically showing another example of thearrangement patterns of cell groups in the honeycomb structure of thepresent invention;

FIG. 11C is a plan view schematically showing still another example ofthe arrangement patterns of cell groups in the honeycomb structure ofthe present invention;

FIG. 11D is a plan view schematically showing a further example of thearrangement patterns of cell groups in the honeycomb structure of thepresent invention;

FIG. 12A is an explanatory view schematically showing a manufacturingstep of one embodiment of the honeycomb structure of the presentinvention;

FIG. 12B is an explanatory view schematically showing a manufacturingstep of the one embodiment of the honeycomb structure of the presentinvention; and

FIG. 12C is an explanatory view schematically showing a manufacturingstep of the one embodiment of the honeycomb structure of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described. Itshould be understood that the present invention is not limited to thefollowing embodiments and that the following embodiments, to whichchanges, improvements and the like are suitably added on the basis ofordinary knowledge of a person skilled in the art without departing fromthe scope of the present invention, also fall in the gist of the presentinvention.

[1] Honeycomb Structure:

One embodiment of a honeycomb structure of the present invention is ahoneycomb structure 100 shown in FIG. 1. The honeycomb structure 100includes a honeycomb substrate 10 having partition walls 1 defining aplurality of cells 2, and plugging portions 25 disposed at open ends ofthe cells 2 of the honeycomb substrate 10. The partition walls 1 definethe plurality of cells 2 which form through channels for a fluid andextend from an inflow end face 11 as one end face where the fluid flowsin to an outflow end face 12 as the other end face where the fluid flowsout. The plurality of cells 2 include at least one cell group 5including three cells which are a both-end plugged cell 2 b in which theplugging portions 25 are disposed at both open ends on the inflow endface 11 side and the outflow end face 12 side, and an inlet cell 2 a andan outlet cell 2 c which are adjacent to the both-end plugged cell 2 b.The inlet cell 2 a is adjacent to the both-end plugged cell 2 b, and hasthe plugging portion 25 disposed only on the outflow end face 12 side ofthe open ends. The outlet cell 2 c is adjacent to the both-end pluggedcell 2 b, and has the plugging portion 25 disposed only on the inflowend face 11 side of the open ends. That is, one both-end plugged cell 2b is adjacent to an inlet cell 2 a and an outlet cell 2 c. The partitionwalls 1 defining the both-end plugged cell 2 b constituting the cellgroup 5 have a first common partition wall 1 a and a second commonpartition wall 1 b. The first common partition wall 1 a is the commonpartition wall 1 defining both of the inlet cell 2 a and the both-endplugged cell 2 b. The second common partition wall 1 b is the commonpartition wall 1 defining both of the outlet cell 2 c and the both-endplugged cell 2 b. A first flow-through hole 7 is formed in an endportion of the first common partition wall 1 a on the outflow end face12 side, and a second flow-through hole 8 is formed in an end portion ofthe second common partition wall 1 b on the inflow end face 11 side.

In the honeycomb structure 100 shown in FIG. 1 and FIG. 2, through-cellswhich are non-plugged cells (i.e., cells whose both open ends areopened) are not present, and hence deterioration of a trappingefficiency due to the presence of the through-cells can be prevented.That is, more suitable trapping efficiency can be obtained than ahoneycomb structure in which one open end or the other open end of eachcell is plugged; such a honeycomb structure as described in PatentDocuments 3 and 4.

Furthermore, the honeycomb structure 100 inhibits an increase of apressure loss when ash is accumulated. As a result, for the honeycombstructure 100, maintenance operations when the ash is accumulated areperformed less times, and the maintenance operations may scarcely beneeded to be performed. That is, the honeycomb structure 100 isso-called free of maintenance in regard to deposition of ash.Specifically, in the honeycomb structure 100, the ash is easilydeposited at two positions; at an end portion on the outflow end face 12side (shown by symbol “X” in FIG. 2) and at an end portion on the inflowend face 11 side (shown by symbol “Y” in FIG. 2), which are in throughchannels formed along a route of inlet cell 2 a, both-end plugged cell 2b and outlet cell 2 c. On the other hand, in a conventional honeycombstructure (such a honeycomb structure as described in Patent Document1), ash is easily deposited only in an end portion on the outflow endface side. That is, the honeycomb structure 100 has a large space wherethe ash can be deposited. Consequently, the honeycomb structure 100 hasa smaller degree of increase of pressure loss as compared with theconventional honeycomb structure, even when the amount of ash as much ascan be deposited under predetermined conditions in the conventionalhoneycomb structure is accumulated in the present honeycomb structure.Furthermore, the ash accumulated in the honeycomb structure 100 suitablyjoins a flow of an exhaust gas to be discharged outside. For example,the ash present in the inlet cell 2 a flows into the both-end pluggedcell 2 b from the first flow-through hole 7 formed in the partition wall1 between the inlet cell 2 a and the both-end plugged cell 2 b. Next,the ash flows into the outlet cell 2 c from the second flow-through hole8 formed in the partition wall 1 between the both-end plugged cell 2 band the outlet cell 2 c. Afterward, the ash is discharged from thehoneycomb structure 100. In this way, the ash can be deposited in thelarge space and the accumulated ash joins the flow of the exhaust gas tobe suitably discharged. Hence the through channels of the exhaust gaswould not completely be closed, and the degree of increase of pressureloss due to the deposition of ash is reduced (increase of pressure lossis inhibited).

FIG. 1 is a perspective view schematically showing one embodiment of thehoneycomb structure of the present invention. FIG. 2 is a sectional viewschematically showing a cross section parallel to an extending directionof cells in the one embodiment of the honeycomb structure of the presentinvention.

The inlet cells, the both-end plugged cells and the outlet cells arepreferably arranged as follows. That is, in a cross section of thehoneycomb substrate which is perpendicular to the cell extendingdirection, a center of the inlet cell is “a first center”, a center ofthe both-end plugged cell is “a second center”, and a center of theoutlet cell is “a third center”. Then, the inlet cell, the both-endplugged cell and the outlet cell are preferably arranged so that thefirst center, the second center and the third center are positioned on asame straight line. In the honeycomb structure 100, the inlet cell 2 a,the both-end plugged cell 2 b and the outlet cell 2 c are arranged sothat the center of the inlet cell 2 a (first center), the center of theboth-end plugged cell 2 b (second center) and the center of the outletcell 2 c (third center) are positioned on the same straight line.

Furthermore, in another preferable configuration, the inlet cell, theboth-end plugged cell and the outlet cell are arranged to form anL-shape as shown in FIG. 4A to FIG. 4H, when seen from the cellextending direction. That is, in this preferable configuration, the cellgroup consisting of three cells of one inlet cell, one both-end pluggedcell and one outlet cell is formed into the L-shape.

That “the inlet cell, the both-end plugged cell and the outlet cell formthe L-shape” indicates that the respective cells are arranged in a statewhere the first common partition wall and the second common partitionwall are not in such a positional relation as to face each other, butare positioned to form two adjacent partition walls among the partitionwalls constituting the both-end plugged cell.

FIG. 4A is a plan view schematically showing an example of arrangementpatterns of a cell group in the honeycomb structure of the presentinvention. FIG. 4B is a plan view schematically showing another exampleof the arrangement patterns of a cell group in the honeycomb structureof the present invention. FIG. 4C is a plan view schematically showingstill another example of the arrangement patterns of a cell group in thehoneycomb structure of the present invention. FIG. 4D is a plan viewschematically showing a further example of the arrangement patterns of acell group in the honeycomb structure of the present invention. FIG. 4Eis a plan view schematically showing a further example of thearrangement patterns of a cell group in the honeycomb structure of thepresent invention. FIG. 4F is a plan view schematically showing afurther example of the arrangement patterns of a cell group in thehoneycomb structure of the present invention. FIG. 4G is a plan viewschematically showing a further example of the arrangement patterns of acell group in the honeycomb structure of the present invention. FIG. 4His a plan view schematically showing a still further example of thearrangement patterns of a cell group in the honeycomb structure of thepresent invention.

The honeycomb structure of the present invention includes at least onecell group. That is, in the honeycomb structure of the presentinvention, the cell group as one set of three cells consisting of theinlet cell, the both-end plugged cell and the outlet cell may partiallybe present. Also when the above cell group is partially present, theadvantageous effect of the present invention can be expected. When thecell group is partially present, for example, in a configuration, thecell groups are disposed in the central portion of the honeycombstructure (central portion in the cross section perpendicular to thecell extending direction), and the cells described below (through-cellsor conventional type cells) are disposed in the outer circumferentialportion (portion other than the central portion). That is, the cellsdisposed in the outer circumferential portion of the honeycomb structuremay be cells which have no plugging portions at both ends(through-cells) or cells having plugging portions in a checkered patternin both the end faces, only in the inflow end face, or only in theoutflow end face (conventional type cells). The latter cells(conventional type cells) are the cells in which the plugging portionsare disposed as in the conventional type honeycomb structure.Furthermore, the abovementioned arrangements in the central portion andthe outer circumferential portion of the honeycomb structure may bereversed. In the honeycomb structure of the present invention, the“ratio of the cell groups” may suitably be determined in considerationof the required trapping efficiency or pressure loss. The ratio ispreferably from 10 to 100% and further preferably from 30 to 100%. The“ratio of the cell groups” is the ratio of “number of the cell groups”to “value of ⅓ of the number of all the cells (number of all the cellsregardless of the presence/absence of the plugging portions”. It is tobe noted that the cells are counted excluding cells deformed by acircumferential wall or cells in which one or more sides (walls) formingeach of the cells constitute the circumferential wall (hereinafter,these cells may be referred to as “incomplete cells”).

When a plurality of cell groups are included, there is not any specialrestriction on an arrangement pattern of these cell groups, but theplurality of cell groups can be arranged as shown in, for example, FIG.5A to FIG. 11D. It is to be noted that in FIG. 5A to FIG. 11D, “1”indicates the inlet cells. “2” indicates the both-end plugged cells. “3”indicates the outlet cells. Furthermore, FIG. 5A to FIG. 11Dschematically show the arrangement patterns of the cell groups, and forthe convenience in explaining the arrangement pattern of the cellgroups, a part of the honeycomb structure is extracted and shown.Additionally, in FIG. 5A to FIG. 11D, depiction of the plugging portionsis omitted.

Each of FIG. 5A to FIG. 11D is a plan view schematically showing thearrangement patterns of cell groups in the honeycomb structure of thepresent invention.

FIG. 5A and FIG. 5B show examples where the cell groups each includingthe inlet cell, the both-end plugged cell and the outlet cell arrangedon the same straight line are arranged in a same order. FIG. 6A and FIG.6B show examples where each of the arrangements shown in FIG. 5A andFIG. 5B is shifted as much as one cell (to the left side or the rightside in the drawing or to the upside or the downside in the drawing)every row. FIG. 7A, FIG. 7B and FIG. 8 show examples where the number ofthe cells to be shifted (to the left side or the right side in thedrawing) is changed in respective rows on the basis of the arrangementshown in FIG. 5A. FIG. 9 and FIG. 10 show examples where the cell groupsshown in FIG. 4A, FIG. 4B and FIG. 4E are alternately arranged.

Furthermore, in the honeycomb structure of the present invention, asshown in FIG. 11A to FIG. 11D, the cell groups each including the inletcell, the both-end plugged cell and the outlet cell arranged on a samestraight line may be arranged while shifting as much as ½ cell to thehorizontal direction of the drawing (to the left side or the right sidein the drawing) every row.

In FIG. 5A and FIG. 5B among FIG. 5A to FIG. 8 and FIG. 11A to FIG. 11D,the inlet cell, the both-end plugged cell and the outlet cell arearranged on a straight line, respectively, and hence the pluggingportions are easily formed which facilitates preparation.

In FIG. 6A, FIG. 6B and FIG. 8, all of four partition walls of eachinlet cell are adjacent to the both-end plugged cell or the outlet cell,and hence the exhaust gas also flows through these partition walls.Therefore, in the arrangements (arrangement patterns) shown in FIG. 6A,FIG. 6B and FIG. 8, the pressure loss lowers as much as about 5% ascompared with the other arrangement patterns.

In addition, a plurality of types of arrangement patterns shown in FIG.5A to FIG. 11D may be combined and arranged.

An open area of the first flow-through hole is preferably from 0.3 to3.5 times and further preferably from 0.5 to three times as large as anaverage value of sectional areas of the inlet cell, the both-end pluggedcell and the outlet cell constituting the cell group. When the above“open area of the first flow-through hole” is smaller than the abovelower limit value, there is the fear that the pressure loss increases.When the above “open area of the first flow-through hole” is in excessof the above upper limit value, there is the fear that isostaticstrength deteriorates. The “sectional areas of the inlet cell, theboth-end plugged cell and the outlet cell” are the areas of therespective cells in the cross section perpendicular to the cellextending direction. In the present description, the “average value ofthe sectional areas of the inlet cell, the both-end plugged cell and theoutlet cell constituting the cell group” is the following value. Thatis, the above average value is a value obtained by multiplying a valueof the sum of “sectional area of the inlet cell”, “sectional area of theboth-end plugged cell” and “sectional area of the outlet cell”constituting one cell group by ⅓. It is to be noted that when the openarea is calculated, a plurality of cell groups are suitably selected.

The “end portion on the outflow end face side” in which the firstflow-through hole is formed is specifically a portion from the outflowend face of the honeycomb structure to a position of ⅓ of the length ofthe honeycomb structure in the cell extending direction (firstflow-through hole forming region). The first flow-through hole ispreferably formed in the above first flow-through hole forming region,but in the above first flow-through hole forming region, the hole ismore preferably formed in a portion from the outflow end face of thehoneycomb structure to a position of ⅕ of the length of the honeycombstructure in the cell extending direction.

An open area of the second flow-through hole is preferably from 0.3 to3.5 times and further preferably from 0.5 to three times as large as theaverage value of the sectional areas of the inlet cell, the both-endplugged cell and the outlet cell constituting the cell group. When theabove “open area of the second flow-through hole” is smaller than theabove lower limit value, there is the fear that the pressure lossincreases. When the above “open area of the second flow-through hole” isin excess of the above upper limit value, there is the fear that theisostatic strength deteriorates.

The “end portion on the inflow end face side” in which the secondflow-through hole is formed is specifically a portion from the inflowend face of the honeycomb structure to the position of ⅓ of the lengthof the honeycomb structure in the cell extending direction (secondflow-through hole forming region). The second flow-through hole ispreferably formed in the above second flow-through hole forming region,but in the above second flow-through hole forming region, the hole ismore preferably formed in a portion from the inflow end face of thehoneycomb structure to the position of ⅕ of the length of the honeycombstructure in the cell extending direction.

There is not any special restriction on a shape of the opening of eachof the first flow-through hole and the second flow-through hole, and theshapes of the openings of the respective flow-through holes may be thesame or different. Examples of the shape of the opening of eachflow-through hole include a circular shape, a semicircular shape, anelliptic shape, a semi-elliptic shape (shape obtained by cutting anellipse along a short diameter), a triangular shape and a quadrangularshape. FIG. 3 shows the enlarged first flow-through holes 7. The shapeof the opening of the first flow-through holes 7 is semi-elliptic. Sucha semi-elliptic opening is easily formed. FIG. 3 is an enlarged viewschematically showing an enlarged part of a cross section perpendicularto the cross section (cross section A-A) shown in FIG. 2.

The honeycomb structure of the present invention is preferably made of aporous ceramic material. That is, the honeycomb substrate and theplugging portions constituting the honeycomb structure are preferablymade of the porous ceramic material. When the honeycomb structure ismade of the porous ceramic material, catalyst is easily loaded onto thehoneycomb structure. The honeycomb structure of the present inventionmay be made of a sintered metal obtained by forming and then sinteringmetal powder, or a metal foil.

Specifically, when the honeycomb structure is made of a ceramicmaterial, the ceramic material is further preferably at least oneselected from the group consisting of cordierite, silicon carbide, asilicon-silicon carbide based composite material, mullite, alumina,aluminum titanate, silicon nitride, and a silicon carbide-cordieritebased composite material, from the viewpoint that the materials areexcellent in strength and heat resistance. Among these materials,cordierite and silicon carbide are preferable.

The honeycomb substrate of the honeycomb structure of the presentinvention preferably has a segment structure constituted of a pluralityof honeycomb segments. Such segment structure enables manufacturing ahoneycomb structure which is hard to be integrally manufactured (e.g.,large honeycomb structure).

The honeycomb substrate having the segment structure can specifically bea bonded assembly having a plurality of honeycomb segments and a bondinglayer to bond the plurality of honeycomb segments to one another.

In addition, the honeycomb substrate of the honeycomb structure of thepresent invention is also preferably integrally formed. The honeycombsubstrate integrally formed in this manner, simplifies the manufacturingsteps. When the honeycomb substrate is “integrally formed”, it is meantthat the honeycomb substrate is constituted of one member. That is, thewhole honeycomb substrate is formed at a time by a method of extrusionor the like.

The respective members of the honeycomb structure of the presentinvention will further be described in the following.

[1-1] Honeycomb Substrate:

A thickness of the partition walls of the honeycomb substrate 10 ispreferably from 40 to 600 μm, further preferably from 80 to 500 μm andespecially preferably from 100 to 400 μm. When the above thickness ofthe partition walls is smaller than 40 μm, there is the fear that thestrength of the partition walls may be insufficient. On the other hand,when the thickness is in excess of 600 μm, there is the fear that thepressure loss increases.

A porosity of the partition walls of the honeycomb substrate 10 ispreferably from 25 to 80%, further preferably from 30 to 75% andespecially preferably from 30 to 70%. When the above porosity is smallerthan 25%, there is the fear that the pressure loss increases. On theother hand, when the porosity is in excess of 80%, there is the fearthat the strength of the partition walls may be lower. Here, in thepresent description, “porosity” is a value measured by a mercuryporosimeter.

An average pore diameter of the partition walls of the honeycombsubstrate 10 is preferably from 5 to 100 μm, further preferably from 7to 80 μm and especially preferably from 7 to 60 When the above averagepore diameter is smaller than 5 μm, there is the fear that the pressureloss increases. On the other hand, when the average pore diameter is inexcess of 100 μm, there is the fear that the exhaust gas purificationperformance deteriorates. Here, in the present description, “the averagepore diameter” is a value measured by the mercury porosimeter.

A cell density of the honeycomb substrate 10 is preferably from 12 to200 cells/cm², further preferably from 15 to 150 cells/cm² andespecially preferably from 20 to 120 cells/cm². When the above celldensity is smaller than 12 cells/cm², there is the fear that theisostatic strength lowers. On the other hand, when the cell density isin excess of 200 cells/cm², there is the fear that the pressure lossincreases.

A shape of each of the cells 2 in the cross section perpendicular to theextending direction of the cells 2 of the honeycomb substrate 10 can be,for example, quadrangular or hexagonal.

A length of the honeycomb substrate 10 (honeycomb structure 100) in thecell extending direction can be from 50 to 1000 mm or more (in excess of1000 mm) In addition, when each end face of the honeycomb structure 100is circular, a diameter of the end faces can be from 25 to 600 mm ormore (in excess of 600 mm).

A shape of the honeycomb substrate 10 can be each of various shapes suchas a columnar shape, an elliptic columnar shape, a quadrangular columnarshape and a hexagonal columnar shape. Among these shapes, the columnarshape and the quadrangular columnar shape are preferable.

[1-2] Plugging Portion:

A depth of each plugging portion (length in the cell extendingdirection) is preferably from 0.3 to 10 mm, further preferably from 0.5to 8 min and especially preferably from 1 to 7 mm. When the depth of theplugging portion is smaller than the above lower limit value, there isthe fear that the plugging portions drop out due to vibrations or thelike. When the depth of the plugging portion is in excess of the aboveupper limit value and the honeycomb structure is used as a filter, thereis the fear that portions of the honeycomb structure functioning as thefilter decrease.

A material of the plugging portions can be the same as the material ofthe partition walls. In particular, the material of the pluggingportions is preferably a porous ceramic material.

The honeycomb structure 100 shown in FIG. 1 has a circumferential wall26, but does not necessarily have the circumferential wall 26. Thecircumferential wall 26 can be formed by applying an outer circumferencecoating ceramic material to an outer circumference of the honeycombstructure. Furthermore, the circumferential wall 26 may be formedsimultaneously with the partition walls in a process of preparing thehoneycomb substrate 10, when the honeycomb substrate is integrallyformed by extrusion or the like.

[2] Manufacturing Method of Honeycomb Structure:

The honeycomb structure of the present invention can be manufactured,for example, as follows. The honeycomb structure in which the honeycombsubstrate is integrally formed will be described.

First, a kneaded material to prepare the honeycomb substrate is preparedand this kneaded material is formed to prepare a honeycomb formed body(forming step).

Next, the obtained honeycomb formed body (or a honeycomb dried bodyafter drying is performed as required) is fired to prepare a honeycombfired body (honeycomb fired body preparing step).

Next, the prepared honeycomb fired body 50 is disposed so that the endportion thereof on the outflow end face 112 side is positioned on theupside as shown in FIG. 12A. Afterward, a resin member is pushed intoeach partition wall 3 in which a first flow-through hole is to beformed. Afterward, the honeycomb fired body 50 is inverted and disposedso that the end portion thereof on the inflow end face 111 side ispositioned on the upside. Afterward, as shown in FIG. 12B, a resinmember 20 is pushed into each partition wall 3 in which a secondflow-through hole is to be formed, so that a portion of the partitionwall 3 into which the resin member 20 is pushed is destroyed. It is tobe noted that the partition walls 3 are very thin, and hence the resinmembers 20 can be pushed thereinto by manual force. When the resinmembers are used in this manner, the flow-through holes (firstflow-through holes and second flow-through holes) each having adesirable size can surely be formed. That is, each resin member performsa function of a spacer, and the resin members burn away when fired, sothat the flow-through holes (first flow-through holes and secondflow-through holes) are formed.

There is not any special restriction on physical properties of the resinmember, as long as the resin member performs the function as spacer andburns away when fired. As to a hardness of the resin member, the resinmember may be hard to such an extent that a part of partition wall maybe destroyed. It is to be noted that when the partition wall ispartially destroyed, the resin member is not directly pushed, but theresin member may be pushed by using a needle, laser beams or the like.In this case, the hardness of the resin member can freely be set, andthe resin member does not have to be hard to such an extent that thepartition wall can be destroyed.

Specifically, as the resin member, a member made of polyethylene, amember made of nylon or the like may be used.

Next, as shown in FIG. 12C, in the honeycomb fired body 50 into whichthe resin members 20 has been pushed, a plugging material 23 is chargedinto spaces formed by pushing the resin members 20 thereinto (pluggingmaterial charging step).

It is to be noted that in the manufacturing method of the honeycombstructure of the present invention, a method without using the resinmembers may be employed. That is, a viscosity of the plugging materialmay be increased, so that each portion that becomes the flow-throughhole is not closed with the plugging material, when the pluggingmaterial is charged thereinto.

Next, the honeycomb fired body into which the plugging material ischarged is fired again to form the plugging portions (plugging portionforming step). The resin members burn away when fired in this manner,and portions where the resin members have been disposed become the firstflow-through holes and the second flow-through holes. In such a manner,the honeycomb structure can be prepared.

In addition, the honeycomb structure may be prepared by grindingpartition walls of the honeycomb dried body dried after forming or byburning using laser beams to form the flow-through holes each having thedesirable size, and then charging the plugging material so that theportions which become the flow-through holes are not closed, followed bythe firing.

EXAMPLES

Hereinafter, the present invention will specifically be described on thebasis of examples, but the present invention is not limited to theseexamples.

Example 1

A pore former, an organic binder and water were added to a cordieriteforming raw material to obtain a forming raw material. The forming rawmaterial was mixed and kneaded to prepare a columnar kneaded material.As an organic binder, methylcellulose was used, and 5 parts by mass ofmethylcellulose was added to 100 parts by mass of the cordierite formingraw material. The water was added as a dispersing medium as much as 10mass % to the whole forming raw material. The cordierite forming rawmaterial is a raw material which becomes cordierite when fired.Specifically, the cordierite forming raw material is a ceramic rawmaterial obtained by mixing “predetermined raw materials” to obtain achemical composition in which silica (SiO₂) is in a range of 42 to 56mass %, alumina (Al₂O₃) is in a range of 30 to 45 mass %, and magnesia(MgO) is in a range of 12 to 16 mass %. “The predetermined rawmaterials” are raw materials selected from the group consisting of talc,kaolin, calcinated kaolin, alumina, aluminum hydroxide and silica.

Next, the kneaded material was extruded by using a predetermined die toobtain a honeycomb formed body having partition walls defining aplurality of cells and a circumferential wall formed simultaneously withthe partition walls by the extrusion. In the honeycomb formed body, thecell shape (shape of each cell in the cross section perpendicular to theextending direction of the cells) was square and the whole shape wascolumnar.

Next, the obtained honeycomb formed body was dried by dielectric dryingand hot air drying, and then fired at the highest temperature of 1420°C. for 100 hours to prepare a honeycomb fired body.

The obtained honeycomb fired body had a partition wall thickness of 100μm and a cell density of 45 cells/cm². Furthermore, the porosity of thepartition walls of the honeycomb fired body was 50%. In addition, theaverage pore diameter of the honeycomb fired body was 18 μm. Thehoneycomb fired body had a columnar shape having a bottom surfacediameter of 320 mm and a length of 300 mm in the cell extendingdirection. Additionally, the porosity and the average pore diameter werevalues measured by a mercury porosimeter.

Next, resin members made of polyethylene were pushed from the inflow endface side along the cell extending direction into the honeycombstructure so as to destroy predetermined end portions of partitionwalls, thereby removing portions (inflow end portions) from thepartition wall. Afterward, portions (outflow end portions) of thepartition wall on the outflow end face side were similarly removed.

Next, plugging material was charged into parts of region formed byremoving the portions from the partition wall so that holes where theadjacent cells communicate with each other are left. That is, theplugging material was charged into each cell at a depth smaller than thedepth of the removed portion. Afterward, the firing was performed again.In this way, the honeycomb structure made of a porous ceramic materialwas prepared.

The prepared honeycomb structure was such a honeycomb structure as shownin FIG. 1. The arrangement pattern of cell groups was such a pattern asshown in FIG. 5A. Specifically, inlet cells, both-end plugged cells andoutlet cells were arranged so that centers of the three cellsconstituting each cell groups were positioned on a same straight line.Furthermore, a plurality of cell groups was present and the cell groupswere vertically and horizontally aligned and arranged.

The open area of each first flow-through hole was 0.3 times as large asthe average value of the sectional areas of the inlet cells, theboth-end plugged cells and the outlet cells constituting the cellgroups. Furthermore, the open area of each second flow-through hole was0.3 times as large as the average value of the sectional areas of theinlet cells, the both-end plugged cells and the outlet cellsconstituting the cell groups. As to the calculation of the above openareas, 20 cell groups were randomly selected.

In addition, the ratio of the cell groups was 100%. It is to be notedthat the ratio of the cell groups is a ratio of “number of the cellgroups” to “value of ⅓ of the number of all the cells”. Furthermore,when the “number of the cell groups” is counted, a same cell is notcounted twice. That is, it can be considered that the “number of thecell groups” is the number of the both-end plugged cells. It is to benoted that when the cells are counted, cells deformed by thecircumferential wall or cells in which one or more sides forming eachcell constitute a part of the circumferential wall (incomplete cells)are excluded. Furthermore, the shape of the opening of each of the firstflow-through holes and second flow-through holes was quadrangular. Thewidth of the opening of the flow-through hole was the same as the widthof the inner dimension of each cell. Specifically, the partition walldestroyed by pushing the resin member made of polyethylene into thehoneycomb structure as described above had a state where a part of thepartition wall did not remain in the form of a so-called burr. It is tobe noted that it can be considered, for example, that FIG. 3 shows astate where a part of each partition wall remains in the form of theso-called burr.

Next, as to the obtained honeycomb structure, “trapping efficiency”,“initial pressure loss” and “pressure loss after ash deposition” weremeasured and evaluated by the following methods. The results are shownin Table 1.

[Trapping Efficiency]

An exhaust gas (200° C.) including soot generated by a “soot generatorwhich burns diesel fuel (light oil), thereby generating soot” wasallowed to pass the honeycomb structure. The soot included in theexhaust gas before the exhaust gas passed the honeycomb structure wastrapped with filter paper, and the weight (W1) of the soot was measured.The soot included in the exhaust gas which passed the honeycombstructure was trapped with filter paper, and the weight (W2) of the sootwas measured. The obtained (W1) and (W2) were substituted into Equation(1) described below, to obtain the trapping efficiency (%).

((W1−W2)/W1)×100  Equation (1)

Afterward, the trapping efficiency was evaluated on the basis of thefollowing standards. When the trapping efficiency improves as much as15% or more as compared with trapping efficiencies of correspondingcomparative examples each having plugging portions only at the inflowend face or only at the outflow end face (shown by “TE1 to TE6” in Table2), the evaluation is “A”. When the improvement is 10% or more andsmaller than 15%, the evaluation is “B”. When the improvement is 5% ormore and smaller than 10%, the evaluation is “C”. When the improvementis smaller than 5%, the evaluation is “D”. It is to be noted that theimprovement of the trapping efficiency of 5% or more can usually beconsidered to be preferable (practical). The results are shown in Table1.

[Initial Pressure Loss]

Air was allowed to flow through the honeycomb structure at anatmospheric pressure (1 atm), room temperature (20° C.) and a rate of 15m³/minute to measure the “initial pressure loss”. Afterward, the initialpressure loss was evaluated on the basis of the following standards.

When the initial pressure loss decreases as much as 30% or more ascompared with pressure losses of corresponding comparative examples eachhaving plugging portions in end portions on both of the inlet side andthe outlet side (shown by “PD1 to PD3” in Table 2), the evaluation is“A”. When the decrease is smaller than 30% and 15% or more, theevaluation is “B”. When the decrease is smaller than 15% and 5% or more,the evaluation is “C”. When the decrease is smaller than 5%, theevaluation is “D”. It is to be noted that the decrease of the initialpressure loss of 5% or more can usually be considered to be preferable(i.e., practical). The results are shown in Table 1.

[Pressure Loss after Ash Deposition]

Ash discharged from engine was collected in advance, for example, at theabove evaluation tests, which is prepared for use. First, in a statewhere the inflow end face of the honeycomb structure was disposed toface upside, 100 g of the ash was supplied into the honeycomb structurefrom the inflow end face. Next, this honeycomb structure was attached toan exhaust tube of a six-cylinder 6,000 cc diesel engine, and operatedon conditions of 2,000 rpm and 100 N-m. After ten minutes from the startof the engine, “initial pressure loss after ash deposition” wasmeasured. Afterward, the initial pressure loss after ash deposition wasevaluated on the basis of the following standards. When the “initialpressure loss after ash deposition” increases as much as 5% or less fromthe “initial pressure loss”, the evaluation is “A”. When the increase isin excess of 5% and 10% or less, the evaluation is “B”. When theincrease is in excess of 10% and 20% or less, the evaluation is “C”.When the increase is in excess of 20%, the evaluation is “D”. Anincrease of 20% or less can be considered to be practical. The resultsare shown in Table 1.

TABLE 1 Arrangement Partition wall Open area of first Open area ofInitial pattern of cell thickness Cell density flow-through second flow-Trapping pressure Pressure loss after Structure groups (μm) (cells/cm²)hole (times) through hole (times) efficiency loss ash deposition Example1 Integral FIG. 5A 140 65 0.3 0.3 A C B Example 2 Integral 140 65 0.50.5 A B A Example 3 Integral 140 65 0.5 1.0 A A A Example 4 Integral 14065 1.0 0.5 A A A Example 5 Integral 140 65 1.0 1.0 A A A Example 6Integral 140 65 2.0 2.0 A A A Example 7 Integral 140 65 3.0 3.0 A A AExample 8 Integral 140 65 3.5 3.5 B A A Example 9 Integral FIG. 6A 25035 0.5 0.5 A B A Example 10 Integral 250 35 3.0 3.0 A A A Example 11Integral FIG. 8  140 65 0.3 0.3 A C B Example 12 Integral 140 65 1.0 1.0A A A Example 13 Integral FIG. 9  250 35 0.3 0.3 A C B Example 14Integral 250 35 1.0 1.0 A A A Example 15 Integral FIG. 11C 140 65 0.30.3 A C B Example 16 Integral 140 65 0.5 0.5 A B A Example 17 Integral140 65 2.0 3.0 A A A Example 18 Integral 140 65 3.5 3.5 B A A Example 19Segment FIG. 7A 250 35 0.3 0.3 A C B Example 20 Segment 250 35 1.0 1.0 AA A Example 21 Segment FIG. 10 250 35 1.0 2.0 A A A Example 22 Segment250 35 3.5 3.5 B A A

In the honeycomb structure of the present example, the evaluation of“trapping efficiency” was “A”, the evaluation of “initial pressure loss”was “C”, and the evaluation of “pressure loss after ash deposition” was“B”.

In Tables 1 and 2, “integral” in the column of “structure” indicatesthat the honeycomb structure is constituted of one extruded structure asin the present example. “Segment” in the column of “structure” indicatesthat the honeycomb structure is constituted by bonding a plurality ofsegment honeycomb structures with a bonding material.

Examples 2 to 22 and Comparative Examples 0.1 to 9

First, in Examples 2 to 18, the procedures of Example 1 were repeated toprepare honeycomb structures satisfying conditions shown in Tables 1 and2.

In each of Examples 19 to 22, segment honeycomb structures each having across section of vertical size 40 mm×horizontal size 40 mm and length300 mm were prepared. The prepared segment honeycomb structures werebonded with a bonding material to prepare a bonded honeycomb assembly,and the outer circumference of this bonded honeycomb assembly wasground. Afterward, an outer circumference coating having a thickness of1 mm was further applied to prepare a honeycomb structure having adiameter of 320 mm and a length of 300 mm. Additionally, the thicknessof the bonding material was 1 mm.

Comparative Examples 1 to 9 were honeycomb structures which have noflow-through holes to allow adjacent cells to communicate with eachother or no both-end plugged cells having both end portions plugged.Furthermore, such honeycomb structures are conventional type honeycombstructures having plugging portions in a checkered pattern at both endfaces, only in an inflow end face, or only in an outflow end face.Comparative Examples 1 to 3 are comparative examples corresponding toExamples 1 to 8, 11, 12 and 15 to 18. Comparative Examples 4 to 6 arecomparative examples corresponding to Examples 9, 10, 13 and 14.Comparative Examples 7 to 9 are comparative examples corresponding toExamples 19 to 22.

Additionally, as to “trapping efficiency”, evaluation was performed onthe basis of a comparative example which has a better trappingefficiency (i.e., having a larger trapping efficiency) of the twocomparative examples corresponding to the example and each havingplugging portions “only at the inflow end face” or “only at the outflowend face”. For example, the trapping efficiency of the honeycombstructure of Example 1 was evaluated on the basis of the honeycombstructure of Comparative Example 2 or 3 having a larger trappingefficiency TE1 or TE2.

As to each of the above honeycomb structures, the procedures of Example1 were repeated to measure and evaluate “trapping efficiency”, “initialpressure loss” and “pressure loss after ash deposition”. The results areshown in Tables 1 and 2. In Table 2, “both end faces” in the column of“arrangement of plugging portions” indicate that plugging portions areformed in end portions of predetermined cells on the inflow end faceside and end portions of the residual cells on the outflow end face sidewherein the plugging portions are arranged alternately (in a zigzagmanner) so as to form so-called checkered patterns at both of the endfaces. In Table 2, “inflow end face only” in the column of “arrangementof plugging portions” indicates that the plugging portions are disposedonly in the end portions on the inflow end face side, and the pluggingportions are not disposed in the end portions on the outflow end faceside wherein the above plugging portions are arranged to form theso-called checkered pattern in the inflow end face. In Table 2, “onlythe outflow end face” in the column of “the arrangement of the pluggingportions” indicates that the plugging portions are disposed only in theend portions on the outflow end face side, the plugging portions are notdisposed in the end portions on the inflow end face side wherein theabove plugging portions are arranged to form the so-called checkeredpattern at the outflow end face.

TABLE 2 Partition wall Initial thickness Cell density Arrangement ofTrapping pressure Structure (μm) (cells/cm²) plugging portionsefficiency loss Comparative Integral 140 65 Both end face — PD1 Example1 Comparative Integral 140 65 Inflow end face only TE1 — Example 2Comparative Integral 140 65 Outflow end face TE2 — Example 3 onlyComparative Integral 250 35 Both end face — PD2 Example 4 ComparativeIntegral 250 35 Inflow end face only TE3 — Example 5 ComparativeIntegral 250 35 Outflow end face TE4 — Example 6 only ComparativeSegment 250 35 Both end face — PD3 Example 7 Comparative Segment 250 35Inflow end face only TE5 — Example 8 Comparative Segment 250 35 Outflowend face TE6 — Example 9 only

It has been confirmed that the honeycomb structures of Examples 1 to 22have improved initial pressure loss and trapping efficiency as comparedwith the honeycomb structures of Comparative Examples 1 to 9.Furthermore, it can be confirmed that the pressure loss after ashdeposition increases less and maintenance operations to be performedwhen the ash is accumulated is not required. Additionally, after thetest, each honeycomb structure was disassembled to observe the insidesof the cells. A small amount of ash has been deposited, and it can beconsidered that most of the ash has been discharged together with theexhaust gas from the engine.

INDUSTRIAL APPLICABILITY

A honeycomb structure of the present invention can be used as a filterto purify exhaust gas discharged from a car or the like.

DESCRIPTION OF SYMBOLS

1 and 3: partition wall, 1 a: first common partition wall, 1 b: secondcommon partition wall, 2: cell, 2 a: inlet cell, 2 b: both-end pluggedcell, 2 c: outlet cell, 5: cell group, 7: first flow-through hole, 8:second flow-through hole, 10: honeycomb substrate, 11: inflow end face,12 and 112: outflow end face, 20: resin member, 23: plugging material,25: plugging portion, 26: circumferential wall, 50: honeycomb firedbody, and 100: honeycomb structure.

What is claimed is:
 1. A honeycomb structure comprising: a honeycombsubstrate having partition walls defining a plurality of cells whichform through channels for a fluid and extend from an inflow end face asone end face where the fluid flows in to an outflow end face as theother end face where the fluid flows out; and plugging portions disposedat open ends of the cells of the honeycomb substrate, wherein the cellsinclude at least one cell group consisting of three cells which are aboth-end plugged cell in which the plugging portions are disposed atboth open ends on the inflow end face side and the outflow end faceside, an inlet cell which is adjacent to the both-end plugged cell andin which the plugging portion is only disposed at the open end on theoutflow end face side, and an outlet cell which is adjacent to theboth-end plugged cell and in which the plugging portion is only disposedat the open end on the inflow end face side, the partition wallsdefining the both-end plugged cell constituting the cell group have afirst common partition wall which is a common partition wall definingboth of the inlet cell and the both-end plugged cell, and a secondcommon partition wall which is a common partition wall defining both ofthe outlet cell and the both-end plugged cell, a first flow-through holeis formed in an end portion of the first common partition wall on theoutflow end face side, and a second flow-through hole is formed in anend portion of the second common partition wall on the inflow end faceside.
 2. The honeycomb structure according to claim 1, wherein in across section of the honeycomb substrate which is perpendicular to anextending direction of the cells, the inlet cell, the both-end pluggedcell and the outlet cell constituting each of the at least one cellgroup are arranged so that a first center which is the center of theinlet cell, a second center which is the center of the both-end pluggedcell and a third center which is the center of the outlet cell arepositioned on a same straight line.
 3. The honeycomb structure accordingto claim 1, wherein in the cross section of the honeycomb substratewhich is perpendicular to the extending direction of the cells, theinlet cell, the both-end plugged cell and the outlet cell constitutingeach of the at least one cell group are arranged to form an L-shape. 4.The honeycomb structure according to claim 1, wherein an open area ofthe first flow-through hole is from 0.3 to 3.5 times as large as anaverage value of sectional areas in the direction perpendicular to thecell extending direction of the inlet cell, the both-end plugged celland the outlet cell constituting the cell group.
 5. The honeycombstructure according to claim 2, wherein an open area of the firstflow-through hole is from 0.3 to 3.5 times as large as an average valueof sectional areas in the direction perpendicular to the cell extendingdirection of the inlet cell, the both-end plugged cell and the outletcell constituting the cell group.
 6. The honeycomb structure accordingto claim 3, wherein an open area of the first flow-through hole is from0.3 to 3.5 times as large as an average value of sectional areas in thedirection perpendicular to the cell extending direction of the inletcell, the both-end plugged cell and the outlet cell constituting thecell group.
 7. The honeycomb structure according to claim 1, wherein anopen area of the second flow-through hole is from 0.3 to 3.5 times aslarge as the average value of the sectional areas in the directionperpendicular to the cell extending direction of the inlet cell, theboth-end plugged cell and the outlet cell constituting the cell group.8. The honeycomb structure according to claim 2, wherein an open area ofthe second flow-through hole is from 0.3 to 3.5 times as large as theaverage value of the sectional areas in the direction perpendicular tothe cell extending direction of the inlet cell, the both-end pluggedcell and the outlet cell constituting the cell group.
 9. The honeycombstructure according to claim 3, wherein an open area of the secondflow-through hole is from 0.3 to 3.5 times as large as the average valueof the sectional areas in the direction perpendicular to the cellextending direction of the inlet cell, the both-end plugged cell and theoutlet cell constituting the cell group.
 10. The honeycomb structureaccording to claim 1, which is made of a porous ceramic material. 11.The honeycomb structure according to claim 1, wherein the honeycombsubstrate is integrally formed.
 12. The honeycomb structure according toclaim 1, wherein the honeycomb substrate has a segment structureconstituted of a plurality of honeycomb segments.